In the field of air-conditioning for industrial vehicles there is a particular need for air-conditioning in the cab even during the stops of the vehicle. Various systems have been proposed for driving the compressor of the refrigeration circuit; when the vehicle is running, said compressor can be driven by the vehicle's main engine, or by an electric motor, which can be operated for example by the current supplied by the usual vehicle's batteries, or by another source of electric power. Systems have been proposed featuring an auxiliary generator set comprising an internal combustion engine of adequate power, which runs on the same fuel as the vehicle's main engine. Indeed, the vehicle's batteries are usually insufficient to guarantee operation in case of prolonged stops it must be avoided to completely discharge the batteries.
However, the systems according to the known art have drawbacks in that it is not easy to reconcile the dimensions of the various elements with an adequate power of the electric motor, in order to guarantee adequate air-conditioning even in the most critical conditions when the main engine is not running. Furthermore, it would be desirable to achieve a better exploitation of the electric machine to drive the compressor, especially if used with batteries or ultracapacitors.